16 October, 2009

Lately my in-box has been overflowing with questions about bottom brackets. So I thought I'd write this simple guide that I can later forward to those seeking advice. Of course this is only about square taper cranks and BBs.

What spindle length?

I often get questions such as, "What is the proper BB spindle length for a 1954 Urago mixte?" Come on; I'm not Sheldon Brown! In any case, the length of your BB spindle is determined largely by the model of crank you use, not by the type of bike. Every crank's manufacturer recommends a BB type and length. Of course, if the crank is long out of production, a lengthy conversation with Google may be required to find the specification.

As with anything, it's not quite that simple. There are a couple of other factors that can influence spindle length. If your bike has particularly wide chain stays, such as those on a mountain bike or a loaded tourer, a longer spindle may be require in order to ensure that the crank arms clear the chain stays. Often, the only way to be sure is to install the crank and see if the BB works. If not, measure the interference or gap and buy a second BB. Unfortunately BBs that have been installed are not returnable, but there is always E-bay. The other factor that might influence spindle length is BB spindle taper.

Spindle taper

The vast majority of square taper cranks uses either an ISO or a JIS taper. Basically, the angle of these two types is almost identical. It's just that a different portion of the taper is used, as I've tried to show in my sketch.

For the most part, today only the Italians use ISO and the rest of the world uses JIS. But there are exceptions, such as the top-of-the-line Sugino track cranks; all other Sugino cranks are JIS. Some older cranks from Stronglight, TA, and other European companies also used ISO tapers. Only Ofmega and Avocet, of the major manufacturers, used a proprietary taper.

It's usually possible to fit an ISO crank on a JIS BB. The only caveat is that the crank will be 3-4mm wider than if an ISO BB was used, so pick a slightly narrower spindle and tighten the crank bolts securely.

I don't recommend using a JIS crank on an ISO spindle because the crank may bottom out, thus permanently ruining the taper. If, however, you are careful, it will work with some combinations.

One of the problems with this whole idea is that manufacturers sometimes take a casual attitude toward toward following one standard or the other. I have seen TA cranks, for example, that appear to be ISO and an identical crank that's JIS, or perhaps something in between.

BB threading

Let us begin with the French standard because this is, after all, Velo Orange. The French decided that BB shells should be 68mm wide, threading should be35mm x 1mm, and both cups should tighten to the right. Simple and effective! Of course VO makes French BBs.

The Swiss improved the French standard by reversing the thread on the non-drive side. This became the Swiss standard and was adopted not only by Swiss manufacturers but also by a few French companies, notably Motobecane. (Motobecane also used French threading on occasion and later switched to British threading; good luck.) The BB shell is 68mm wide and also threaded 35mm X 1mm; but the left cup tightens to the right and the right to the left.

The reason for this improved standard was that the spinning of the crank was thought to loosen the right-hand thread non-drive BB cups. After a few decades, the Swiss noticed that French cyclists, in fact, were not stopping every few miles to tighten their cups. And so the standard was quietly abandoned. The only Swiss threaded BBs made today are the super expensive Phil Wood units. But in a few weeks VO will have a threadless BB that will be a less expensive alternative.

The French standard was also eventually abandoned and, to the everlasting annoyance of the French and of francophiles everywhere, the British (or ISO) standard became the world standard. If your frame was made in America, Japan, Taiwan, Germany, or Britain, it almost certainly accepts a British threaded BB. This standard is 1.375" X 24 tpi with the left cup tightening to the right and the right to the left; the BB shell is 68mm wide. Most VO BBs are British thread.

Not leaving well enough alone, some British manufacturers, particularly Raleigh, came up with other standards that are outside of my understanding, as did some old American manufacturers.

Finally the Italians, who we reluctantly acknowledge do know something about bicycles, if only the racing sort, blithely ignored everyone else and stuck to their own standard. The Italian BB shell is 70mm wide and has 36 mm X 24 tpi threading; both cups tighten to the right. VO does not make Italian threaded BBs, but they are widely available.

So there you have it, a gross oversimplification of BB standards that should, nonetheless, provide sufficient information to fit 99% of traditional frames with BBs.

Nice to read that you like the background. The design is pretty close to what I envisioned, just a few tweeks with fonts and colors, details that drive me nuts. Kyle did the html and Trygva did the link bar at the top.

A French threaded headset is in the works. We just paid way too much for tooling to have the proper French-style washers made again. The old tooling was tossed years ago. As soon as I get a sample washer I'll OK production. It'll be just like the alloy VO ball bearing headset.

What I have never understood is why bicycles abandoned metric standards (at least in bottom bracket, pedal and headset threading) for Imperial ones while the rest of the world was going to, or had already arrived at, metric standards.

Hello anyone/everyone! Your help would be greatly appreciated! I have a NOS TA Pro 5 Vis BSC crankset and don't know if the cranks are ISO or JIS. They measure 14mm wide on the inside and taper to 13mm.Thanks!

I always thought it was the drive side cups that loosened, not the off drive side (or at least that's what happened on my gitane tandem (both BBs) and my peugeot folder) Of course, it only happens if you don't tighten them securely, say because they often come with wrench flats too large for my crescent wrench and too small for my bottom bracket wrenches.

I admit I'm one who has tampered with the tapers and boggled over brackets. I've tried a few with TA Pro Vis 5 laser etched cranks with double ring. TA Axix Ti 115mm (wonderfully light, smooth turning and simple), TA 344 115mm (the proper equipment) and Phil's 116mm R+5mm (the finest equipment). The Axix didn't clear my chain stay on the drive side, the 344 works to near perfection and remains installed with a small q-factor on a 130mm spaced frame and generous tyre clearance. The Phil is not yet installed but looks to provide the most flexibility, having a 5mm+/- tuning and a 5mm offset just like the TA 344. I'll install that one day because it feels so nice to spin and I can adjust the position in the shell.

The TA 344 drive side cup has loosened before. It also takes 10 balls as opposed to 11 on the non-drive side. One set of TA Pro Vis 5 crank arms I have are labeled G1/BSC/170. I thought BSC referred to the taper type?

I'm now intimately acquainted with my own bicycle's BB needs. Probably the single best way to be when solving it's problems.

Thanks for the BB information posting. Well done with the web stuff too!

ATB shell width is 73mm, but intermittently so. as for clockwise threading on 35 x 1" bb's, i've definitely seen serially loosening french drive side cups. it doesn't happen that often, but the theoretical principle is the same as with side-specific pedal threading. there's no reason to think that cartridge bb's would loosen however, because the balls aren't directly contacting the threaded cup. typically all you need is a good amount of torque to set it beyond whatever backward pressures the balls can exert at their outer edges. the Var tool is superb for this.

also, anybody ever tried to ram an avocet crank onto something? ISO spindle perhaps? those cranks are too beautiful not to be used.

i have avocet cranksets on two bikes; i've heard you can use older campy bbs (nuovo and super record) with them, but with the two i had there was a good 1/4" of crank taper left unseated when a nr bb was used. the avocet and ofmega cx bbs are identical and they show up fairly regularly on the dreaded ebay and are usually cheap. just takes some patience. i have an avocet 70 width spindle for a triple if you need one.

I've seen Italian thread frames where the threads were a bit worn and the R side cups didn't want to stay put. The solution is to run cartridge BB's and just install them from the L side. This also works to get a good 42mm chainline for fixed gear or whatever with the RD2 crank -- it's supposed to take a 103mm spindle, which nobody makes for Italian, so you just run a 107 in from the L side with a spacer under it, et voila!

How can one properly install a BB from the L side without turning it around? If that is the case the newer cartridge BB's have plastic cups which I wouldn't think would be good on the drive side or R side... Lastly, what is the spacer under it you speak of? I am wishing to keep a 42mm chainline but like you said no one makes a 103mm spindle for Italian!

Toast ghost and Perry:Your discussion about Avocet/Ofmega has me intrigued, because I've got an old "Avocet 3" bottom bracket with Avocet triple crankset, and want very much to use them.Trouble is, I have one threaded bearing assembly (English thread, apparently), and nothing for the other side. I'm very dumb about this. What can I buy and where to make this crankset usable? The side I have is pretty sluggish from hardened old grease and could be overhauled, but I'd sooner buy the pair. Is it possible? So I've got the correct spindle and the matching cranks, but need the rest.Thanks, and excuse my ignorance.Chas

The problem with the drive side cup loosening is not typically caused by any reverse force of the rotating balls. The cup would have to be quite loose for this to occur. The problem is due to the slight clearance that is built in between the outer thread of the cup and the inner thread of the BB shell. There is a tolerance for this clearance, so it is different for any frame/BB combination. Try placing a cylindrical object inside a larger ring and then roll the cylinder around, keeping it in contact with the ring. You will notice that the cylinder rotates in the opposite direction. This is why French and Italian BB right cups have the nasty propensity to loosen up. With a strong enough rider, even a solidly tightened right cup can loosen up, providing the clearance is great enough. Once it loosens, it will start walking its way out of the frame, and it's not an easy thing to thread it back in when you're out on the road without the necessary tools. The fanciful description of Swiss engineers noticing that French BBs don't loosen up is not at all accurate. The Swiss solution was an elegant way to solve a known problem with French BBs, while sticking with metric sizing. It's too bad that everyone didn't adopt the Swiss standard, but that would have made too much sense. The real reason the Swiss standard died out was that the British standard had too much inertia behind it for the Swiss standard to get purchase in the market, and the Swiss just gave up and adopted the British standard.